This invention relates to a gear transmission with overtop or overdrive for automotive vehicles. More particularly, this invention relates to a gear transmission having an overdrive gear mechanism mounted within an extension housing immediately after the rear end wall of a transmission case.
It has been advantageous to incorporate an overtop gear mechanism between a countershaft and an output shaft of a gear transmission in order to permit the engine to operate at a lower speed than that of a propeller shaft during vehicular operation at a high speed. This feature reduces fuel consumption as well as minimizing vibrations. However, gear transmissions of this type have been mounted only on the so-called sport cars in which the gear transmission is directly controlled, and not mounted on commercial cars having a remote-controlled type of gear transmission.
In general, the conventional gear transmissions with overdrive are of the five-speed and reverse type in which the fifth or overdrive gear shift position is located opposite to the fourth gear shift position, the fourth gear being a position at which the output shaft rotates at the same speed with that of the input shaft of the gear transmission. The overtop gear mechanism is mounted in an extension housing so that the gear transmission case and the transmission gears set therein may be compatible for both the conventional four-speed gear transmission and the five-speed gear transmission with overdrive.
Problems have been encountered in the conventional gear transmissions with overdrive of the type described. In general, an additional countershaft must be provided in order to mount a countershaft overdrive gear. The extension housing provided must also be bulged in order to enclose therein a countershaft overdrive gear of a large diameter. A shift reversing mechanism must be additionally mounted in order to make the gear shift lever direction the same as the actuating direction for engaging the overdrive gear to the output shaft.
Accordingly, it is a primary object of this invention to incorporate an overtop or overdrive gear mechanism in a remotely controlled type of gear transmission. Another object of this invention is to provide a new and improved gear transmission that eliminates the problems encountered in the conventional directly controlled or operated gear transmissions with overdrive.
Still another object of this invention is to provide a new and improved gear transmission with overdrive without an additional countershaft or shift reversing mechanism.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the gear transmission of this invention comprises: (1) a transmission case having front and rear end walls; (2) an input shaft and an output shaft rotatably and coaxially disposed within the transmission case, the input shaft extending through the front end wall of the transmission case and the output shaft extending through the rear end wall of the transmission case; (3) a countershaft rotatably disposed within the transmission case and parallel to the input and output shafts, the countershaft extending through the rear end wall of the transmission case; (4) a pair of drive gears, the first one mounted on the input shaft and the second one mounted on the countershaft, meshed with each other for transmitting the torque from the input shaft to the countershaft; (5) a plurality of pairs of transmission gears of different gear ratios for obtaining different speed ratios of the input shaft to the output shaft, the first gear of each pair of transmission gears being rigidly mounted on the countershaft and the second gear of each pair being rotatably mounted on the output shaft, the gears of each pair being meshed with each other; (6) a plurality of synchronizer assemblies mounted on the output shaft and selectively actuated for engagement with the transmission gears rotatably mounted on the output shaft for coupling one of the first transmission gears to the output shaft; (7) an overdrive mechanism including (a) a pair of overdrive gears, the first one rigidly mounted on the countershaft and the second one rotatably mounted on the output shaft, meshed with each other, and (b) an overdrive synchronizer assembly having a first part mounted on the output shaft and a second part fixedly mounted with respect to the first part, the first part being selectively actuated for engagement with the first overdrive gear for coupling the overdrive gear to the output shaft, the gear ratio of the overdrive gears being such that when the first overdrive gear is coupled to the output shaft, the output shaft is rotated at a higher rotational speed than the input shaft; and (8) a gear shift mechanism for selectively actuating one of the transmission synchronizer assemblies or the overdrive synchronizer assembly for changing the speed ratio of the input shaft to the output shaft as the gear transmission is shifted from one gear position to another.
The invention consists in the novel parts, constructions, arrangements, combinations and improvements shown and described. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and, together with the description, serve to explain the principles of the invention.